Semi-bright copper



United States Patent No Drawing. Filed .iuly 14, 1960, Ser. No. 42,755 8Claims. (Cl. 204-52) The present invention is directed to alkalinecyanide copper plating baths and more particularly to semi-bright bathshaving a leveling or smoothing eifect to reduce surface micro-roughness.

In certain applications of copper deposits it is more desirable toobtain leveling than to obtain a high degree of brightness. Of thebright cyanide copper baths in the prior art, none had the ability ofdepositing coatings which would hide or level surface imperfections onthe basis metal without using periodic reverse currents. Actually, suchprior baths often exerted a negative leveling; i.e., they magnified theimperfections. The prior art addition agents further tended toaccentuate the negative leveling effect of the bath. It is known thatthe prior art acid copper plating baths can be made to level or reducesurface roughness of the basis metal when certain organic additionagents are incorporated in the bath. For instance, such acid baths arecapable of reducing the surface roughness of a comparatively roughsurface to R.M.S. value of about 30.

On the other hand, the prior art cyanide copper baths even with additionagents were unable to reduce surface roughness or hide imperfections oncomparatively smooth surfaces (R.M.S. values of 10 or below) unlessperiodic reverse current was used. The baths described in this inventionare capable of producing positive leveling in cyanide copper bathswithout the use of periodic reverse current on surfaces that had initialroughness of approximately 10 R.M.S. or less. If periodic reversecurrent is utilized with the baths of this invention, then the degree ofleveling becomes considerably enhanced, in fact far better than thatsecured from prior art periodic reverse cyanide copper baths.

The present invention is intended and adapted to overcome thedeficiencies and disadvantgaes inherent in cyanide copper plating baths,it being among the objects thereof to introduce into such baths anaddition agent which will have a leveling effect on a copper depositwithout using periodic reverse current, to eliminate surface roughnessof about 10-15 R.M.S. and lower.

It is also among the objects of the invention to provide a bath of thecharacter described which is adapted to produce a crystal structure ofthe deposited copper which, while only semi-bright, can be readilybrightened by the subsequent bright nickel coatings.

It is further among the objects of the invention to provide a bath ofsuch character that even if the copper deposit is burned, the subsequentnickel coating tends to brighten readily.

' ing or leveling eifect and brighten the deposit. The bright- It isstill further among the objects of the invention to provide a cyanidecopper bath that will produce leveling with or without reverse currentfrom the same bath.

In practicing the present invention there is provided the usual cyanidecopper plating baths, for instance:

G./l. CuCN 45-75 Total KCN 75-120 KOH 15-30 ness approximates thatobtained by the practice of US. Patent No. 2,287,654, describing the useof ,thiocyanate in the bath, which has no leveling elfect withoutperiodic reverse current. Actually in such prior baths, selenium orsulfur in the 2 state and tellurium in the 2 and +4 state, destroyleveling when present in concentrations required or recommended to givefull or maximum brightness of the deposit.

The compounds which are the addition agents of the present invention areof the type set forth in Table I below:

The compounds of the present invention may be included in the followinggeneral formula:

wherein R is a hydrocarbon radical having 2 to 3 carbon atoms, X ishydrogen or [OR] OH and n is 0 to 20.

The leveling efiect of the above class of compounds is enhanced by thepresence of a small amount of zinc in the soluble form, such as sodiumzincate or zinc cyanide. In high efliciency cyanide copper baths theconcentration of the zinc in the range of 0.01 to 1.0 g./l. givesexcellent results. The optimum range is between 0.1 and 0.2 g./l.

In order to obtain good leveling it is important that the bath contain alimited concentration of the selenium, tellurium, or sulfur typebrighteners. Selenium having a valence of -2, sulfur in the sulfidestate and tellurium should not be present in amounts exceeding 0.0005g./l. However, controlled amounts of selenium (in the -2 state) orsulfidic sulfur may be utilized within the above limits, say from 0.0001to 0.0005 g./l. whereby increased brightness of deposit is obtainedwithout impairing appreciably the micro-leveling characteristic of thebath.

Table II attached hereto contains a number of specific examples whichwill illustrate the nature of the invention.

ROX

ROX

Table 11 CuCN .l- 60 75 45 75 60 75 6O 60 i 94 KOH 15 20 15 30 30 15 1515' Znaszineateor Cyanie 0.2 0.3 0.15 0.2 0.5 0.4

The Plating is conducted at temperatures of 7 1 5. A plating bathaccording to claim 1 characterized in F. with a current density of 10 to40 amperes per square foot. Mild to vigorous agitation is provided.

Among the present addition agents, those of larger molecular weight orof more complex structure are preferred'. Those hydroxy polyamines whichhave ether linkages have a greater leveling efiect than those which donot contain such ether linkages. Mixtures of hydroxy 'polyamines aremore effective than single compounds.

While the amounts used may vary from 0.01 to 50.0 g./l., it is preferredto employ from 0.5 to 10.0 g./l, in most applications.

The present cyanide baths exhibit micro-leveling whereas the acid copperbaths exhibit macro-leveling. However, it is possible to obtain microaswell as macroleveling from these cyanide baths by utilizing periodicreverse current.

' We claim: 7

1. An aqueous alkaline cyanide copper plating bath having incorporatedtherein a compound having the following formula:

/R 0 X -RN X-O R BOX wherein R represents a hydrocarbon radical havingfrom 2 to 3 carbon atoms, X represents hydrogen and -[OR] -OH, and n is0 to 20, the amount of said compound present in the bath beingsufiicient to produce micro-leveling in the deposit.

2. A plating bath according to claim 1 characterized in that the amountof said compound is about 0.1 to 50.0 g./l.

3. A plating bath according to claim 1 characterized in that said bathcontains less than 1.0 g./l. of a soluble zinc salt.

4. A plating bath according to claim 1 characterized in that said bathcontains about 0.01 to 1.0 g./l. of a soluble zinc salt.

that said bath is substantially free from soluble compounds of selenium,tellurium and sulfur.

' 6. A plating bath according to claim 1 characterized in that said bathcontains not over 0.0005 g./l. of soluble compounds of selenium,tellurium and sulfur.

"I. A plating bath according to claim 1 characterized in thatsaidcompound has from 1 to 4 free OH groups.

and at least one ether group.

' References Cited in the file of this patent UNITED STATES PATENTSPortzer Nov. 26, 1957 Winters May 6, 1958

1. AN AQUEOUS ALKALINE CYANIDE COPPER PLATING BATH HAVING INCORPORATEDTHEREIN A COMPOUND HAVING THE FOLLOWING FORMULA: